Normally physics proxy will be one frame ahead of the render geometry due to multithreading, which means aiming at the render proxy can miss. Also, pe_status_pos will be guaranteed to return the same coords that were set by a preceding pe_params_pos, even if the command was queued and isn't fully executed yet.
This feature optionally keeps a second set of top-level entity coordinates (pos+quat) that is synchronized to the main set when a logged poststep event is sent (in the main thread), meaning it's in sync with the main CEntity coordinates. World queries (RWI, PWI, GEA) can optionally do tests using these coordinates. Also, pe_params_pos requests modify them instantly, and pe_status_pos can optionally read them instead of the main coordinates (meaning that SetParams(pe_params_pos); GetStatus(pe_status_pos); will return the updated position even if SetParams was queued).